Multi-scale investigation of morphological, physical and tensile properties of flax single fiber, yarn and unidirectional fabric

In this study, the morphological, physical, and tensile properties of flax were experimentally investigated at three different scales (single fiber, yarn and unidirectional fabric). The cross-sectional area was determined directly using microscopic image and indirectly via linear density with gravimetric and vibroscopic methods. All specimens were tested in tension until failure. The results showed that measured properties and their variability were scale-dependent. The tensile strength and modulus of elasticity were gradually decreasing with the scale and the variabilities were decreasing when going from fibers to yarns and fabric. This difference in the properties should be considered for any multi-scale analysis of the flax reinforcement. The average failure strains of single fiber, yarn and fabric were 2% (±30%), 1.7% (±12%) and 1.7% (±2.8%), respectively. Due to the consistency of failure strain at different material scales, it can be recommended as design criterion. The results of this study can be used for better design and preparation of plant-based natural fiber reinforced polymer composites.